/*
 * Copyright (C) 2010 The Android Open Source Project
 * Copyright (C) 2012 Google Inc.
 *
 * Licensed under the Apache License, Version 2.0 (the "License");
 * you may not use this file except in compliance with the License.
 * You may obtain a copy of the License at
 *
 *      http://www.apache.org/licenses/LICENSE-2.0
 *
 * Unless required by applicable law or agreed to in writing, software
 * distributed under the License is distributed on an "AS IS" BASIS,
 * WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
 * See the License for the specific language governing permissions and
 * limitations under the License.
 */
package com.squareup.moshi;

import java.io.ObjectStreamException;
import java.io.Serializable;
import java.util.*;

/**
 * A map of comparable keys to values. Unlike {@code TreeMap}, this class uses
 * insertion order for iteration order. Comparison order is only used as an
 * optimization for efficient insertion and removal.
 * <p>
 * <p>This implementation was derived from Android 4.1's TreeMap and
 * LinkedHashMap classes.
 */
final class LinkedHashTreeMap<K, V> extends AbstractMap<K, V> implements Serializable {
    @SuppressWarnings({"unchecked", "rawtypes"}) // to avoid Comparable<Comparable<Comparable<...>>>
    private static final Comparator<Comparable> NATURAL_ORDER = new Comparator<Comparable>() {
        @Override
        public int compare(Comparable a, Comparable b) {
            return a.compareTo(b);
        }
    };

    Comparator<? super K> comparator;
    Node<K, V>[] table;
    final Node<K, V> header;
    int size = 0;
    int modCount = 0;
    int threshold;

    /**
     * Create a natural order, empty tree map whose keys must be mutually
     * comparable and non-null.
     */
    LinkedHashTreeMap() {
        this(null);
    }

    /**
     * Create a tree map ordered by {@code comparator}. This map's keys may only
     * be null if {@code comparator} permits.
     *
     * @param comparator the comparator to order elements with, or {@code null} to
     *                   use the natural ordering.
     */
    @SuppressWarnings({
            "unchecked", "rawtypes" // Unsafe! if comparator is null, this assumes K is comparable.
    })
    LinkedHashTreeMap(Comparator<? super K> comparator) {
        this.comparator = comparator != null
                ? comparator
                : (Comparator) NATURAL_ORDER;
        this.header = new Node();
        this.table = new Node[16]; // TODO: sizing/resizing policies
        this.threshold = (table.length / 2) + (table.length / 4); // 3/4 capacity
    }

    @Override
    public int size() {
        return size;
    }

    @Override
    public V get(Object key) {
        Node<K, V> node = findByObject(key);
        return node != null ? node.value : null;
    }

    @Override
    public boolean containsKey(Object key) {
        return findByObject(key) != null;
    }

    @Override
    public V put(K key, V value) {
        if (key == null) {
            throw new NullPointerException("key == null");
        }
        Node<K, V> created = find(key, true);
        V result = created.value;
        created.value = value;
        return result;
    }

    @Override
    public void clear() {
        Arrays.fill(table, null);
        size = 0;
        modCount++;

        // Clear all links to help GC
        Node<K, V> header = this.header;
        for (Node<K, V> e = header.next; e != header; ) {
            Node<K, V> next = e.next;
            e.next = e.prev = null;
            e = next;
        }

        header.next = header.prev = header;
    }

    @Override
    public V remove(Object key) {
        Node<K, V> node = removeInternalByKey(key);
        return node != null ? node.value : null;
    }

    /**
     * Returns the node at or adjacent to the given key, creating it if requested.
     *
     * @throws ClassCastException if {@code key} and the tree's keys aren't
     *                            mutually comparable.
     */
    Node<K, V> find(K key, boolean create) {
        Comparator<? super K> comparator = this.comparator;
        Node<K, V>[] table = this.table;
        int hash = secondaryHash(key.hashCode());
        int index = hash & (table.length - 1);
        Node<K, V> nearest = table[index];
        int comparison = 0;

        if (nearest != null) {
            // Micro-optimization: avoid polymorphic calls to Comparator.compare().
            @SuppressWarnings("unchecked") // Throws a ClassCastException below if there's trouble.
                    Comparable<Object> comparableKey = (comparator == NATURAL_ORDER)
                    ? (Comparable<Object>) key
                    : null;

            while (true) {
                comparison = (comparableKey != null)
                        ? comparableKey.compareTo(nearest.key)
                        : comparator.compare(key, nearest.key);

                // We found the requested key.
                if (comparison == 0) {
                    return nearest;
                }

                // If it exists, the key is in a subtree. Go deeper.
                Node<K, V> child = (comparison < 0) ? nearest.left : nearest.right;
                if (child == null) {
                    break;
                }

                nearest = child;
            }
        }

        // The key doesn't exist in this tree.
        if (!create) {
            return null;
        }

        // Create the node and add it to the tree or the table.
        Node<K, V> header = this.header;
        Node<K, V> created;
        if (nearest == null) {
            // Check that the value is comparable if we didn't do any comparisons.
            if (comparator == NATURAL_ORDER && !(key instanceof Comparable)) {
                throw new ClassCastException(key.getClass().getName() + " is not Comparable");
            }
            created = new Node<K, V>(nearest, key, hash, header, header.prev);
            table[index] = created;
        } else {
            created = new Node<K, V>(nearest, key, hash, header, header.prev);
            if (comparison < 0) { // nearest.key is higher
                nearest.left = created;
            } else { // comparison > 0, nearest.key is lower
                nearest.right = created;
            }
            rebalance(nearest, true);
        }

        if (size++ > threshold) {
            doubleCapacity();
        }
        modCount++;

        return created;
    }

    @SuppressWarnings("unchecked")
    Node<K, V> findByObject(Object key) {
        try {
            return key != null ? find((K) key, false) : null;
        } catch (ClassCastException e) {
            return null;
        }
    }

    /**
     * Returns this map's entry that has the same key and value as {@code
     * entry}, or null if this map has no such entry.
     * <p>
     * <p>This method uses the comparator for key equality rather than {@code
     * equals}. If this map's comparator isn't consistent with equals (such as
     * {@code String.CASE_INSENSITIVE_ORDER}), then {@code remove()} and {@code
     * contains()} will violate the collections API.
     */
    Node<K, V> findByEntry(Entry<?, ?> entry) {
        Node<K, V> mine = findByObject(entry.getKey());
        boolean valuesEqual = mine != null && equal(mine.value, entry.getValue());
        return valuesEqual ? mine : null;
    }

    private boolean equal(Object a, Object b) {
        return a == b || (a != null && a.equals(b));
    }

    /**
     * Applies a supplemental hash function to a given hashCode, which defends
     * against poor quality hash functions. This is critical because HashMap
     * uses power-of-two length hash tables, that otherwise encounter collisions
     * for hashCodes that do not differ in lower or upper bits.
     */
    private static int secondaryHash(int h) {
        // Doug Lea's supplemental hash function
        h ^= (h >>> 20) ^ (h >>> 12);
        return h ^ (h >>> 7) ^ (h >>> 4);
    }

    /**
     * Removes {@code node} from this tree, rearranging the tree's structure as
     * necessary.
     *
     * @param unlink true to also unlink this node from the iteration linked list.
     */
    void removeInternal(Node<K, V> node, boolean unlink) {
        if (unlink) {
            node.prev.next = node.next;
            node.next.prev = node.prev;
            node.next = node.prev = null; // Help the GC (for performance)
        }

        Node<K, V> left = node.left;
        Node<K, V> right = node.right;
        Node<K, V> originalParent = node.parent;
        if (left != null && right != null) {

            /*
             * To remove a node with both left and right subtrees, move an
             * adjacent node from one of those subtrees into this node's place.
             *
             * Removing the adjacent node may change this node's subtrees. This
             * node may no longer have two subtrees once the adjacent node is
             * gone!
             */

            Node<K, V> adjacent = (left.height > right.height) ? left.last() : right.first();
            removeInternal(adjacent, false); // takes care of rebalance and size--

            int leftHeight = 0;
            left = node.left;
            if (left != null) {
                leftHeight = left.height;
                adjacent.left = left;
                left.parent = adjacent;
                node.left = null;
            }
            int rightHeight = 0;
            right = node.right;
            if (right != null) {
                rightHeight = right.height;
                adjacent.right = right;
                right.parent = adjacent;
                node.right = null;
            }
            adjacent.height = Math.max(leftHeight, rightHeight) + 1;
            replaceInParent(node, adjacent);
            return;
        } else if (left != null) {
            replaceInParent(node, left);
            node.left = null;
        } else if (right != null) {
            replaceInParent(node, right);
            node.right = null;
        } else {
            replaceInParent(node, null);
        }

        rebalance(originalParent, false);
        size--;
        modCount++;
    }

    Node<K, V> removeInternalByKey(Object key) {
        Node<K, V> node = findByObject(key);
        if (node != null) {
            removeInternal(node, true);
        }
        return node;
    }

    private void replaceInParent(Node<K, V> node, Node<K, V> replacement) {
        Node<K, V> parent = node.parent;
        node.parent = null;
        if (replacement != null) {
            replacement.parent = parent;
        }

        if (parent != null) {
            if (parent.left == node) {
                parent.left = replacement;
            } else {
                assert (parent.right == node);
                parent.right = replacement;
            }
        } else {
            int index = node.hash & (table.length - 1);
            table[index] = replacement;
        }
    }

    /**
     * Rebalances the tree by making any AVL rotations necessary between the
     * newly-unbalanced node and the tree's root.
     *
     * @param insert true if the node was unbalanced by an insert; false if it
     *               was by a removal.
     */
    private void rebalance(Node<K, V> unbalanced, boolean insert) {
        for (Node<K, V> node = unbalanced; node != null; node = node.parent) {
            Node<K, V> left = node.left;
            Node<K, V> right = node.right;
            int leftHeight = left != null ? left.height : 0;
            int rightHeight = right != null ? right.height : 0;

            int delta = leftHeight - rightHeight;
            if (delta == -2) {
                Node<K, V> rightLeft = right.left;
                Node<K, V> rightRight = right.right;
                int rightRightHeight = rightRight != null ? rightRight.height : 0;
                int rightLeftHeight = rightLeft != null ? rightLeft.height : 0;

                int rightDelta = rightLeftHeight - rightRightHeight;
                if (rightDelta == -1 || (rightDelta == 0 && !insert)) {
                    rotateLeft(node); // AVL right right
                } else {
                    assert (rightDelta == 1);
                    rotateRight(right); // AVL right left
                    rotateLeft(node);
                }
                if (insert) {
                    break; // no further rotations will be necessary
                }

            } else if (delta == 2) {
                Node<K, V> leftLeft = left.left;
                Node<K, V> leftRight = left.right;
                int leftRightHeight = leftRight != null ? leftRight.height : 0;
                int leftLeftHeight = leftLeft != null ? leftLeft.height : 0;

                int leftDelta = leftLeftHeight - leftRightHeight;
                if (leftDelta == 1 || (leftDelta == 0 && !insert)) {
                    rotateRight(node); // AVL left left
                } else {
                    assert (leftDelta == -1);
                    rotateLeft(left); // AVL left right
                    rotateRight(node);
                }
                if (insert) {
                    break; // no further rotations will be necessary
                }

            } else if (delta == 0) {
                node.height = leftHeight + 1; // leftHeight == rightHeight
                if (insert) {
                    break; // the insert caused balance, so rebalancing is done!
                }

            } else {
                assert (delta == -1 || delta == 1);
                node.height = Math.max(leftHeight, rightHeight) + 1;
                if (!insert) {
                    break; // the height hasn't changed, so rebalancing is done!
                }
            }
        }
    }

    /**
     * Rotates the subtree so that its root's right child is the new root.
     */
    private void rotateLeft(Node<K, V> root) {
        Node<K, V> left = root.left;
        Node<K, V> pivot = root.right;
        Node<K, V> pivotLeft = pivot.left;
        Node<K, V> pivotRight = pivot.right;

        // move the pivot's left child to the root's right
        root.right = pivotLeft;
        if (pivotLeft != null) {
            pivotLeft.parent = root;
        }

        replaceInParent(root, pivot);

        // move the root to the pivot's left
        pivot.left = root;
        root.parent = pivot;

        // fix heights
        root.height = Math.max(left != null ? left.height : 0,
                pivotLeft != null ? pivotLeft.height : 0) + 1;
        pivot.height = Math.max(root.height,
                pivotRight != null ? pivotRight.height : 0) + 1;
    }

    /**
     * Rotates the subtree so that its root's left child is the new root.
     */
    private void rotateRight(Node<K, V> root) {
        Node<K, V> pivot = root.left;
        Node<K, V> right = root.right;
        Node<K, V> pivotLeft = pivot.left;
        Node<K, V> pivotRight = pivot.right;

        // move the pivot's right child to the root's left
        root.left = pivotRight;
        if (pivotRight != null) {
            pivotRight.parent = root;
        }

        replaceInParent(root, pivot);

        // move the root to the pivot's right
        pivot.right = root;
        root.parent = pivot;

        // fixup heights
        root.height = Math.max(right != null ? right.height : 0,
                pivotRight != null ? pivotRight.height : 0) + 1;
        pivot.height = Math.max(root.height,
                pivotLeft != null ? pivotLeft.height : 0) + 1;
    }

    private EntrySet entrySet;
    private KeySet keySet;

    @Override
    public Set<Entry<K, V>> entrySet() {
        EntrySet result = entrySet;
        return result != null ? result : (entrySet = new EntrySet());
    }

    @Override
    public Set<K> keySet() {
        KeySet result = keySet;
        return result != null ? result : (keySet = new KeySet());
    }

    static final class Node<K, V> implements Entry<K, V> {
        Node<K, V> parent;
        Node<K, V> left;
        Node<K, V> right;
        Node<K, V> next;
        Node<K, V> prev;
        final K key;
        final int hash;
        V value;
        int height;

        /**
         * Create the header entry.
         */
        Node() {
            key = null;
            hash = -1;
            next = prev = this;
        }

        /**
         * Create a regular entry.
         */
        Node(Node<K, V> parent, K key, int hash, Node<K, V> next, Node<K, V> prev) {
            this.parent = parent;
            this.key = key;
            this.hash = hash;
            this.height = 1;
            this.next = next;
            this.prev = prev;
            prev.next = this;
            next.prev = this;
        }

        @Override
        public K getKey() {
            return key;
        }

        @Override
        public V getValue() {
            return value;
        }

        @Override
        public V setValue(V value) {
            V oldValue = this.value;
            this.value = value;
            return oldValue;
        }

        @SuppressWarnings("rawtypes")
        @Override
        public boolean equals(Object o) {
            if (o instanceof Entry) {
                Entry other = (Entry) o;
                return (key == null ? other.getKey() == null : key.equals(other.getKey()))
                        && (value == null ? other.getValue() == null : value.equals(other.getValue()));
            }
            return false;
        }

        @Override
        public int hashCode() {
            return (key == null ? 0 : key.hashCode())
                    ^ (value == null ? 0 : value.hashCode());
        }

        @Override
        public String toString() {
            return key + "=" + value;
        }

        /**
         * Returns the first node in this subtree.
         */
        public Node<K, V> first() {
            Node<K, V> node = this;
            Node<K, V> child = node.left;
            while (child != null) {
                node = child;
                child = node.left;
            }
            return node;
        }

        /**
         * Returns the last node in this subtree.
         */
        public Node<K, V> last() {
            Node<K, V> node = this;
            Node<K, V> child = node.right;
            while (child != null) {
                node = child;
                child = node.right;
            }
            return node;
        }
    }

    private void doubleCapacity() {
        table = doubleCapacity(table);
        threshold = (table.length / 2) + (table.length / 4); // 3/4 capacity
    }

    /**
     * Returns a new array containing the same nodes as {@code oldTable}, but with
     * twice as many trees, each of (approximately) half the previous size.
     */
    static <K, V> Node<K, V>[] doubleCapacity(Node<K, V>[] oldTable) {
        // TODO: don't do anything if we're already at MAX_CAPACITY
        int oldCapacity = oldTable.length;
        @SuppressWarnings("unchecked") // Arrays and generics don't get along.
                Node<K, V>[] newTable = new Node[oldCapacity * 2];
        AvlIterator<K, V> iterator = new AvlIterator<K, V>();
        AvlBuilder<K, V> leftBuilder = new AvlBuilder<K, V>();
        AvlBuilder<K, V> rightBuilder = new AvlBuilder<K, V>();

        // Split each tree into two trees.
        for (int i = 0; i < oldCapacity; i++) {
            Node<K, V> root = oldTable[i];
            if (root == null) {
                continue;
            }

            // Compute the sizes of the left and right trees.
            iterator.reset(root);
            int leftSize = 0;
            int rightSize = 0;
            for (Node<K, V> node; (node = iterator.next()) != null; ) {
                if ((node.hash & oldCapacity) == 0) {
                    leftSize++;
                } else {
                    rightSize++;
                }
            }

            // Split the tree into two.
            leftBuilder.reset(leftSize);
            rightBuilder.reset(rightSize);
            iterator.reset(root);
            for (Node<K, V> node; (node = iterator.next()) != null; ) {
                if ((node.hash & oldCapacity) == 0) {
                    leftBuilder.add(node);
                } else {
                    rightBuilder.add(node);
                }
            }

            // Populate the enlarged array with these new roots.
            newTable[i] = leftSize > 0 ? leftBuilder.root() : null;
            newTable[i + oldCapacity] = rightSize > 0 ? rightBuilder.root() : null;
        }
        return newTable;
    }

    /**
     * Walks an AVL tree in iteration order. Once a node has been returned, its
     * left, right and parent links are <strong>no longer used</strong>. For this
     * reason it is safe to transform these links as you walk a tree.
     * <p>
     * <p><strong>Warning:</strong> this iterator is destructive. It clears the
     * parent node of all nodes in the tree. It is an error to make a partial
     * iteration of a tree.
     */
    static class AvlIterator<K, V> {
        /**
         * This stack is a singly linked list, linked by the 'parent' field.
         */
        private Node<K, V> stackTop;

        void reset(Node<K, V> root) {
            Node<K, V> stackTop = null;
            for (Node<K, V> n = root; n != null; n = n.left) {
                n.parent = stackTop;
                stackTop = n; // Stack push.
            }
            this.stackTop = stackTop;
        }

        public Node<K, V> next() {
            Node<K, V> stackTop = this.stackTop;
            if (stackTop == null) {
                return null;
            }
            Node<K, V> result = stackTop;
            stackTop = result.parent;
            result.parent = null;
            for (Node<K, V> n = result.right; n != null; n = n.left) {
                n.parent = stackTop;
                stackTop = n; // Stack push.
            }
            this.stackTop = stackTop;
            return result;
        }
    }

    /**
     * Builds AVL trees of a predetermined size by accepting nodes of increasing
     * value. To use:
     * <ol>
     * <li>Call {@link #reset} to initialize the target size <i>size</i>.
     * <li>Call {@link #add} <i>size</i> times with increasing values.
     * <li>Call {@link #root} to get the root of the balanced tree.
     * </ol>
     * <p>
     * <p>The returned tree will satisfy the AVL constraint: for every node
     * <i>N</i>, the height of <i>N.left</i> and <i>N.right</i> is different by at
     * most 1. It accomplishes this by omitting deepest-level leaf nodes when
     * building trees whose size isn't a power of 2 minus 1.
     * <p>
     * <p>Unlike rebuilding a tree from scratch, this approach requires no value
     * comparisons. Using this class to create a tree of size <i>S</i> is
     * {@code O(S)}.
     */
    static final class AvlBuilder<K, V> {
        /**
         * This stack is a singly linked list, linked by the 'parent' field.
         */
        private Node<K, V> stack;
        private int leavesToSkip;
        private int leavesSkipped;
        private int size;

        void reset(int targetSize) {
            // compute the target tree size. This is a power of 2 minus one, like 15 or 31.
            int treeCapacity = Integer.highestOneBit(targetSize) * 2 - 1;
            leavesToSkip = treeCapacity - targetSize;
            size = 0;
            leavesSkipped = 0;
            stack = null;
        }

        void add(Node<K, V> node) {
            node.left = node.parent = node.right = null;
            node.height = 1;

            // Skip a leaf if necessary.
            if (leavesToSkip > 0 && (size & 1) == 0) {
                size++;
                leavesToSkip--;
                leavesSkipped++;
            }

            node.parent = stack;
            stack = node; // Stack push.
            size++;

            // Skip a leaf if necessary.
            if (leavesToSkip > 0 && (size & 1) == 0) {
                size++;
                leavesToSkip--;
                leavesSkipped++;
            }

            /*
             * Combine 3 nodes into subtrees whenever the size is one less than a
             * multiple of 4. For example we combine the nodes A, B, C into a
             * 3-element tree with B as the root.
             *
             * Combine two subtrees and a spare single value whenever the size is one
             * less than a multiple of 8. For example at 8 we may combine subtrees
             * (A B C) and (E F G) with D as the root to form ((A B C) D (E F G)).
             *
             * Just as we combine single nodes when size nears a multiple of 4, and
             * 3-element trees when size nears a multiple of 8, we combine subtrees of
             * size (N-1) whenever the total size is 2N-1 whenever N is a power of 2.
             */
            for (int scale = 4; (size & scale - 1) == scale - 1; scale *= 2) {
                if (leavesSkipped == 0) {
                    // Pop right, center and left, then make center the top of the stack.
                    Node<K, V> right = stack;
                    Node<K, V> center = right.parent;
                    Node<K, V> left = center.parent;
                    center.parent = left.parent;
                    stack = center;
                    // Construct a tree.
                    center.left = left;
                    center.right = right;
                    center.height = right.height + 1;
                    left.parent = center;
                    right.parent = center;
                } else if (leavesSkipped == 1) {
                    // Pop right and center, then make center the top of the stack.
                    Node<K, V> right = stack;
                    Node<K, V> center = right.parent;
                    stack = center;
                    // Construct a tree with no left child.
                    center.right = right;
                    center.height = right.height + 1;
                    right.parent = center;
                    leavesSkipped = 0;
                } else if (leavesSkipped == 2) {
                    leavesSkipped = 0;
                }
            }
        }

        Node<K, V> root() {
            Node<K, V> stackTop = this.stack;
            if (stackTop.parent != null) {
                throw new IllegalStateException();
            }
            return stackTop;
        }
    }

    abstract class LinkedTreeMapIterator<T> implements Iterator<T> {
        Node<K, V> next = header.next;
        Node<K, V> lastReturned = null;
        int expectedModCount = modCount;

        @Override
        public final boolean hasNext() {
            return next != header;
        }

        final Node<K, V> nextNode() {
            Node<K, V> e = next;
            if (e == header) {
                throw new NoSuchElementException();
            }
            if (modCount != expectedModCount) {
                throw new ConcurrentModificationException();
            }
            next = e.next;
            return lastReturned = e;
        }

        @Override
        public final void remove() {
            if (lastReturned == null) {
                throw new IllegalStateException();
            }
            removeInternal(lastReturned, true);
            lastReturned = null;
            expectedModCount = modCount;
        }
    }

    final class EntrySet extends AbstractSet<Entry<K, V>> {
        @Override
        public int size() {
            return size;
        }

        @Override
        public Iterator<Entry<K, V>> iterator() {
            return new LinkedTreeMapIterator<Entry<K, V>>() {
                public Entry<K, V> next() {
                    return nextNode();
                }
            };
        }

        @Override
        public boolean contains(Object o) {
            return o instanceof Entry && findByEntry((Entry<?, ?>) o) != null;
        }

        @Override
        public boolean remove(Object o) {
            if (!(o instanceof Entry)) {
                return false;
            }

            Node<K, V> node = findByEntry((Entry<?, ?>) o);
            if (node == null) {
                return false;
            }
            removeInternal(node, true);
            return true;
        }

        @Override
        public void clear() {
            LinkedHashTreeMap.this.clear();
        }
    }

    final class KeySet extends AbstractSet<K> {
        @Override
        public int size() {
            return size;
        }

        @Override
        public Iterator<K> iterator() {
            return new LinkedTreeMapIterator<K>() {
                public K next() {
                    return nextNode().key;
                }
            };
        }

        @Override
        public boolean contains(Object o) {
            return containsKey(o);
        }

        @Override
        public boolean remove(Object key) {
            return removeInternalByKey(key) != null;
        }

        @Override
        public void clear() {
            LinkedHashTreeMap.this.clear();
        }
    }

    /**
     * If somebody is unlucky enough to have to serialize one of these, serialize
     * it as a LinkedHashMap so that they won't need Gson on the other side to
     * deserialize it. Using serialization defeats our DoS defence, so most apps
     * shouldn't use it.
     */
    private Object writeReplace() throws ObjectStreamException {
        return new LinkedHashMap<K, V>(this);
    }
}
